Today, developers are focused more on providing all Internet Protocol (“IP”) solutions to roaming nodes (e.g., radios, telephones, laptops, personal digital assistants, etc.). As such, it is necessary to have a seamless IP-based mobility solution. Seamless mobility for mobile nodes from one location to another is hence becoming increasingly important. Thus, fast and reliable handoffs for the mobile node are becoming more important.
One of the ways to achieve low latency handoffs is to make use of layer 2 triggers to perform layer 3 handoffs. A pre-registration technique has been proposed in an Internet Draft to address low latency handoffs. The pre-registration technique exploits early triggers from the link layer that indicate a handoff is going to occur. The pre-registration technique uses this early trigger to start the mobile IP registration process from the mobile node's first foreign agent and/or first access node (i.e., current point of attachment), even though the registration itself is in reference to a new point of attachment, e.g. a second foreign agent and/or second access node. This early launch of the mobile IP registration process helps reduce overall handoff delay since more time is provided for the mobile IP registration to complete.
As illustrated in FIG. 1, the first foreign agent 100 acts as a proxy for the second foreign agent 102 so that the mobile node 104 and the first foreign agent 100 can exchange messages on behalf of the second foreign agent 102. It is important to note that where foreign agents are used that the first foreign agent does not generate the messages and simply relays the messages to and from the mobile node 104.
Summarily, where access nodes are used, if a mobile node tries to perform pre-registration for a new co-located care-of-address on a new link, e.g. with a second access node, the mobile node must wait for a timeout before it attempts to register again with a home agent. In such a case, the message sent on the old link may have been lost and so handoff is delayed.
A disadvantage of the pre-registration technique as described in the Internet draft (and as known with access nodes) is that it relies on control signaling between the mobile node 104 and the first foreign agent 100 after the link layer has indicated that a handoff is imminent. In other words, the quality of the air interface link between the mobile node 104 and the first point of attachment, e.g. a first foreign agent 100 is likely deteriorating rapidly. The deterioration of the link between the mobile node 104 and the first point of attachment increases the likelihood of dropped messages. Under these conditions, it may not always be possible for the mobile node 104 to complete the pre-registration process prior to the “link down” with the first point of attachment (e.g., the mobile node 104 may be moving too fast). Under the Internet Draft, when pre-registration fails, the handoff time is longer than with standard mobile IP. This shortcoming makes the pre-registration technique as described in the Internet draft less than desirable, especially for mission critical applications.
Further, in the case of a pre-registration failure, one of the following needs to occur before the mobile node 104 can perform a mobile IP registration: either the registration request timer expires and the mobile node 104 solicits another agent advertisement from the second point of attachment, e.g. second foreign agent 102, or the second point of attachment transmits its regular periodic router and/or agent advertisement. A disadvantage to this technique is that both of these events could take in the order of a second to occur, which would significantly slow the handoff process.
Alternatively, the mobile node 104 could always transmit an agent solicitation upon “link up” with the second point of attachment, and transmit a registration request to the home agent 106 upon receiving the advertisement. If the home agent 106 already has the care of address registered, the home agent 106 would simply refresh the state and send a reply. A disadvantage to this technique is that the number of registration requests could potentially double, which may lead to home agent 106 loading issues. Another disadvantage to this technique is wasted resources in case where the pre-registration succeeds.
Thus, there exists a need for a new method for improving the reliability of low latency handoffs.